(1) Field of the Invention
This invention relates to a mask and method of recovering alignment marks after forming a metal layer on a wafer planarized using chemical mechanical polishing. More particularly the invention relates to dividing a pattern formed on an extra mask and placing the pattern into the end regions of a mask used to pattern the wafer active region.
(2) Description of the Related Art
U.S. Pat. No. 5,271,798 to Sandhu et al. describes a method and apparatus for removing material from alignment marks using local etching. In this method the etchant is confined to the region of the wafer where the alignment marks are located.
U.S. Pat. No. 4,768,883 to Waldo et al. describes an alignment reticle for improving the accuracy of alignment and reducing alignment errors. The invention does not deal with methods of recovering alignment marks obscured by wafer processing steps.
This invention describes a mask pattern and method for recovering alignment marks obscured by wafer process steps which does not require the use of additional reticles. The pattern conventionally placed on separate reticles is divided into two parts and placed in the end regions of the mask used to pattern the active region of the wafer.